1. Field of the Invention
This invention relates to a thermal printer, and, more particularly, it is concerned with an improvement in the thermal printer for better print quality.
2. Description of the Prior Art
It is a usual practice in the thermal printer for printing characters and letters that a thermal head having a vertical row of dots is first heated, and then the thermal head is moved sidewise, while printing. In view of such a printing operation under heat by the thermal head, there tend to occur differences in the running of the printed dots depending on heat generating time, temperature characteristic of the thermal head, paper quality, and so forth, hence it is difficult to maintain constant the size and density of the printed dots. Rather, the difference in density is prone to occur due to density of the printed dots. In order to avoid such a disadvantage, there has been made a correction or adjustment among the horizontal rows (cr rank) of dots relative to the lateral movement of the thermal head.
Of recent, the number of dots in a character tend to increase (e.g., 24.times.24 dots per character) due to printing of complicated character patterns such as chinese characters and so on. With such an increase in the number of dots in one character, the distance among the dots constituting the character becomes shorter. A consequence of which it has become more and more difficult to improve the printed quality of the character without a density adjustment in not only the horizontal row (rank) but also the vertical row (file).